Connector terminals are housed in the terminal housing rooms formed in a housing. The connector terminals are prevented from coming loose by lances which are formed in the terminals housing rooms and which lock the connector terminals. However, downsizing of electrical connector is now advancing, and there is a tendency that the holding force for the connector terminals by the lances alone may become inadequate. Hence, the housing is provided with a retainer, and the connector terminals are doubly locked, thereby enhancing the holding force for the connector terminals.
The electrical connectors that doubly lock the connector terminals are disclosed in, for example, Unexamined Japanese Patent Application Kokai Publication No. S62-64076 (Patent Literature 1), Unexamined Japanese Patent Application Kokai Publication No. 2001-43925 (Patent Literature 2), and Unexamined Japanese Patent Application Kokai Publication No. 2000-208195 (Patent Literature 3).
The electrical connector disclosed in Patent Literature 1, as illustrated in FIG. 23 of the present application, have a stopper lever member 3b and a locking lever member 8b. The stopper lever member 3b is engaged with the connection terminal 2b provided in the housing 1b. The locking lever member 8b extends from the backward side of the housing 1b toward the forward side thereof, and has the front end that is a free end 9b. A user pushes a pushing end 11b to spread the locking lever members 8b outwardly. Thereby, the free end 9b of the locking lever member 8b is engaged with a locking pawl 7b of the connection terminal 2b. 
The electrical connector disclosed in Patent Literature 2, as illustrated in FIGS. 24-25 of the present application, includes a mail terminal holder 103A, a female terminal holder 105A, and a female terminal locking 104A. The female terminal locking 104A is slidable in X-direction and X′ direction.
As shown in FIG. 25 of the present application, the flexible stopper piece 1012 of the female terminal 102A is locked with the engagement tier 1040c. Further, when the user slides the female terminal locking 104A, the vertical wall 1033 of the female terminal locking 104A and the vertical portion 1031a of the frame 31 are engaged with the shoulder portion 1019 of the female terminal 102A, and thus the female terminal 102A is locked.
The electrical connector disclosed in Patent Literature 3, as illustrated in FIG. 26 of the present application, has a side retainer 1130. The side retainer 1130 is slideable between the tentative locking position and the final locking position where the male terminal fitting 111 is engageable.
The slide of the side retainer 1130 is performed by inserting a jig in the operating portion 1135 formed in the side retainer 1130.
According to the electrical connector disclosed in Patent Literature 1, however, when downsizing of the electrical connector advances, the engagement hole of the housing is also downsized. Hence, the fitting work between the locking lever members 8b with the pushing member 10b being held becomes difficult. In addition, when the connection terminal 2b is pulled hard in the pull-out direction, depending on the warpage condition of the locking lever member 8b, the locking of the connection terminal 2b may be released.
In addition, according to the electrical connector disclosed in Patent Literature 2, likewise, when downsizing of the electrical connector advances, the operation lever 1036 becomes tiny, making the user difficult to slide the female terminal locking 104A while holding the operation lever 1036.
Still further, according to the electrical connector disclosed in Patent Literature 3, when the jig is inserted in the retainer, a contact portion of the male terminal fitting 111 and the internal face of the engagement recess 1112 of the outer housing 1110 may be damaged.